Determination of Rb-Sr age for separated chondrules from the Allegan chondrite

Rb-Sr isotopic study as well as petrologic investigations have been done on sixteen individul chondrule samples separated from the Allegan (H5) chondrite. The Rb-Sr chondrule isochron does not define a very precise age (4.42±0.17 Ga) and 87Sr/86Sr initial ratio (0.6997±0.0014) due to the very small variation in Rb/Sr ratio for the chondrules, whereas the model ages give a much more speciffic value (4.42±0.02 Ga). These ages may probably be indicative of the time of primary process (es) (e.g. chondrule formation) rather than secondary (metamorphic reheating) or tertiary (shock heating) processes in and/or on the H-chodrite parent body (or bodies). Chemical compositions of oliveines (Fa=17.5mol%, mean deviation (MD)=1.3%) and orthopyoxenes (Fs=15.4mol%, MD=3.2%) are moderately homogenized among the chondrules, while certains chemically uneguilibrated features are also distinctly preserved in this chondrite. Homogeneity of the mineral compositions, therefore, could not have been caused by thermal metamorphism but were probably inherited from processes prior to aggregation of the components. The overall implications of the chondrule isochron and model ages in relation to the petrological features and in comparison with Rb-Sr data of other chondrites of different chemical groups and petrologic types are discussed

Isotopic Analysis of Rb and Sr Using a Full Automatic Thermal Ionization Mass Spectrometer

Analytical method for strontium isotope ratios and rubidium and strontium concentrations has been established using a full automatic thermal ionization mass spectrometer. The machine is a modified model "MAT 260" of Varian MAT LTD. Each of simultaneously loaded thirteen samples is successively analysed full automatically following to a specific controling program which has been selected as being most suitable for each sample. However, the most characteristic feature of this machine compared to other types is computer controled peak jumping and peak centering before measurment of the signal of each peak. By this the accuracy of isotopic measurement has been surprisingly improved. Analytical procedures are described in detail which include decomposition of samples, separation of Rb and Sr, loading samples on filament and mass spectrometry. Accuracy and reproducibility of isotope analyses are excellent : 43 separate analyses of standard sample NBS 987 over one year gave a mean (87)Sr/(86)Sr ratio of 0.710238 (normalized to the (88)Sr/(86)Sr ratio of 8.375209) with a value of　20δ of 0.000008. The ratio obtained is slightly　higher than the value of 0.71014 given by NBS,　but it is almost identical to the mean of recently　reported twenty analyses. Our determinations for Rb and Sr concentrations of standard samples are as follows : JG-1, Rb 184.4 ppm, Sr 185.5 ppm; JB-l, Rb 41.5Ppm, Sr 448.4 ppm , each of which is near the mean of reported values for corresponding element of the sample (ANDO et al., 1974). Concentrations of Rb and Sr in pure water and regents used in chemical treatement of samples were also measured; a possible error due to the contamination is negligible for most geochemical samples

Rb-Sr age of K-rich LL-chondrite Yamato-74442

Yamato-74442, a brecciated LL-group chondrite, consists of fragments with igeous texture, chondrules, mineral fragments, and host. The fragments involve K-rich fragments as well as normal ones. Typically, both fragments consist mainly of euhedral porphyritic olivines and a few orthopyroxenes in a glassy grundmass. EPMA analyses for these fragments indicate that olivines and orthoptroxenes have a range of Fe/(Fe+Mg) ratio of 27.19～31.33 and 20.10～26.91 mol%, respectively. There is no significant difference in these rations between K-rich (Na2O/K2O<1) and normal framents. The K2O contents of groundmass for K-rich fragments range from 0.51 to 4.89 wt% and that of the normal fragments is 0.38～090 wt%. K2O contents of groundmass vary from fragment to fragment but are rather homegeneous in a single fragment. Rb-Sr isotopic determination on eighteen K-rich fragments (1.5 to 9.5mg in weight) gave an internal isochron age of 4.514±0.022 (2σ) Ga (λ87Rb=1.42×10-11y-1) and initial 87Sr/86Sr ratio of 0.7016±0.0024. This age is somewhat old compared with a whole rock isochron age of LL chondrites (4.493±0.18 Ga; Minster and Allegre, 1981). From a comoarison of the present result with others so far reported, it is inferred that the alkali differentiation as observed in Yamato-74442 probably occurred prior to or during a process of accumulation from LL chondrite parent material in the early solar nebula.

Chemical and Rb-Sr isotopic features of the shock-melted chondrite Yamato-793533

The Sr isotopic compositions and Rb and Sr abundances, as well as major element abundances in olivine, pyroxenes and glass, were determined for a chip and 21 fractions separated from a shock-melted chondrite Yamato-793533, a dark-colored, porous stone with glassy texture. Two lithologies were recognized for the 1.5g specimen studied (Yamato-793533, 67) ; L (Main portion) and L to LL (Dark portion) chondritic in terms of chemical compositions of olivine and pyroxenes. The chemical compositions of glass are relatively homogeneous (SiO2=67-77%) compared to those of other ordinary chondrites, suggesting a moderate cooling rate after shock-melting. The data points for fractions do not foem any isochron in a 87Rb/86Sr vs. 87Sr/86Sr diagram. However, it is noted that six out of nine points for the dark portion plot around a 1.2 Ga line, while most of points for the main portion plot around a 4.55 Ga chondrite isochron. The observed difference could be responsible for difference in melting degrees between the two portions. Similar Rb-Sr features have been found among shock-melted Yamato-79 LL-chondrites which are considered to be paired stones experienced the same shock-melting event at 1.2 Ga. Consequently, the Rb-Sr systematics as well as petrologic features strongly suggest that Yamato-793533 is a member of a series of the shock-melted Yamato-79 LL-chondrites

ガーナ，アシャンティ火山帯南部に分布する古原生代変火山岩類のSr-Nd 同位体組成

Neodymium (Nd) and strontium (Sr) isotopic data are presented for Paleoproterozoic metavolcanic rocks in the southern part of the Ashanti volcanic belt of Ghana. The metavolcanic rocks are predominantly basalts/basaltic andesites and andesites with minor dacites. Two types of basalts/basaltic andesites (B/A), Type I and Type II, have been identified. The Type I B/A are stratigraphically overlain by the Type II B/A, followed by the andesites and the dacites. The analyzed volcanic rocks commonly have low initial (87)Sr/(86)Sr ratios consistent with previous studies on Paleoproterozoic rocks from the West African craton. The LREE-depleted, tholeiitic Type I B/A exhibit back-arc basin geochemical signatures and show high positive epsilon Nd (i.e., ε(Nd) (2.1 Ga) = +3.89 to +7.21), which suggest a long term depleted source and also indicate that they were produced in an entirely oceanic environment devoid of influence of continental crust. The isotope signatures are thus consistent with the previously published trace element data of the Type I basalts/basaltic andesites in suggesting that their parent magma was generated from a depleted mantle. The Type I B/A have Nd model ages (T(DM2)) of 1.83–2.09 Ga similar to their formation ages, suggesting that they were juvenile at their time of formation. The andesites and the Type II B/A andesites show LREE-enriched patterns and exhibit characteristics of subduction zone-related magmas, and show initial ε(Nd) (2.1Ga) values of –1.15 to + 1.35 and Nd model ages (T(DM2)) of 2.32–2.58 Ga. The LREE-enriched dacitic porphyry also exhibits characteristics of subduction zone-related magmas, and have initial ε(Nd) (2.1Ga) value of –2.24 and Nd model ages (T(DM2)) of 2.64 Ga. The Nd isotopic data confirms the juvenile character of the Birimian crust, but also suggests some contributions of a pre-Birimian crustal material (or Archean?) in the genesis of some of the metavolcanic rocks. Our isotopic result is consistent with the island arc complex model which views Paleoproteozoic terranes of West Africa in the context of subduction–accretion processes

Trace element and isotopic characteristics of inclusions in the Yamato ordinary chondrites Y-75097, Y-793241 and Y-794046

Igneous inclusions and hosts of the Yamato ordinary chondrites Y-75097 (L6), Y-793241 (L6) and Y-794046 (H5) were analyzed for lithophile trace elements, and Rb-Sr, rare gas and oxygen isotopes, together with preliminary petrographic examinations. On a three oxygen-isotope plot, all the inclusions lie near the H-chondrite field. The Y-75097 host and inclusion were severely shocked and the Rb-Sr systematics were disturbed by a 500Ma event which was defined by the K-Ar age. The Y-793241 host and inclusion are unshocked and have an old K-Ar age of 4270±170Ma and undisturbed Rb-Sr systematics for the bulk meteorite. Both Y-75097 and Y-793241 inclusions have similar chemical compositions and mineral assemblages consisting mainly of olivine (Fa_), and minor plagioclase (An_), chlor-apatite, merrillite and chromite. Olivines in both inclusions equilibrated with those of their L6 hosts. The two inclusion mantles consisting of mainly olivine and plagioclase show a highly fractionated REE pattern with middle REE depletion and a large positive Eu anomaly (50-100 times chondritic) (V-shaped). A model calculation suggests that this remarkable REE fractionation was produced by thermal equilibration with the phosphate-rich cores of inclusions during the igneous formation and the metamorphic event. The Y-794046 inclusion comprises abundant anhedral olivines (Fa_), fractured pyroxenes (Fs_) and microcrystalline plagioclase (An_Ab_Or_). The inclusion did not equilibrate with its host which has less Fe-rich olivines (Fa_) and more Fe in pyroxenes (Fs_). The inclusion shows an unfractionated REE pattern. We suggest that the three inclusions formed by melting of differentiated precursor materials carrying unfractionated REE. They were then incorporated into the L-or H-chondrite parent bodies and subjected to the early thermal metamorphism, which eventually overprinted the fractionated REE in the Y-75097 and Y-793241 inclusions by solid/solid equilibrium partitioning. The Y-794046 inclusion was subjected to less extensive equilibration, so that REE abundances remained unfractionated

Inhibition of Rho-associated coiled-coil containing protein kinase enhances the activation of epidermal growth factor receptor in pancreatic cancer cells

<p>Abstract</p> <p>Background</p> <p>Rho-associated coiled-coil containing protein kinase (Rho-kinase/ROCK) is involved in various cellular functions including cell proliferation, and is generally considered to be oncogenic, while some studies show that ROCK functions as a negative regulator of cancer progression. As a result, the precise role of ROCK remains controversial. We have previously reported that Rho-kinase/ROCK negatively regulates epidermal growth factor (EGF)-induced cell proliferation in SW480 colon cancer cells. In the present study, we investigated the role of ROCK in EGF receptor (EGFR) signaling in the pancreatic cancer cell lines, Panc1, KP3 and AsPc1.</p> <p>Results</p> <p>In these cells, Y27632, a specific ROCK inhibitor, enhanced EGF-induced BrdU incorporation. The blockade of EGF stimulation utilizing anti-EGFR-neutralizing antibodies suppressed Panc1 cell proliferation. EGF induced RhoA activity, as well as the phosphorylation of cofilin and myosin light chain (MLC), both targets of ROCK signaling, and Y27632 suppressed both of these processes, indicating that the phosphorylation of cofilin and MLC by EGF occurs through ROCK in Panc1 cells. EGF-induced phosphorylation of EGFR at tyrosine residues was augmented when the cells were pretreated with Y27632 or were subjected to gene silencing using ROCK-siRNA. We also obtained similar results using transforming growth factor-α. In addition, EGF-induced phosphorylation of p44/p42 mitogen-activated protein kinase and Akt were also enhanced by Y27632 or ROCK-siRNA. Moreover, an immunofluorescence microscope study revealed that pretreatment with Y27632 delayed EGF-induced internalization of EGFR. Taken together, these data indicate that ROCK functions to switch off EGFR signaling by promoting the internalization of the EGFR.</p> <p>Conclusions</p> <p>While EGF first stimulates the activation of the EGFR and subsequently increases cancer cell proliferation, EGF concurrently induces the activation of ROCK, which then turns off the activated EGFR pathway via a negative feedback system.</p

Development of Strategic Establishment of Technology Bases for a Fusion DEMO Reactor in Japan

The strategic establishment of technology bases required for the development of a fusion demonstration reactor (DEMO) has been discussed by joint endeavors throughout the Japanese fusion community. The mission of Fusion DEMO is to demonstrate the technological and economic feasibility of fusion energy. The basic concept of Fusion DEMO has been identified and the structure of technological issues to ensure the feasibility of this DEMO concept has been examined. The Joint-Core Team consisting of experts from the Japanese fusion community including industry has pointed out that DEMO should be aimed at steady power generation beyond several hundred thousand kilowatts, availability which must be extensible to commercialization, and overall tritium breeding sufficient to achieve fuel-cycle self-sufficiency. The necessary technological issues and activities have been sorted out along with 11 identified elements of DEMO, such as superconducting coils, blanket, divertor, and others. These will be arranged within a time line to lead to the Japanese fusion roadmap

Novel Mouse Xenograft Models Reveal a Critical Role of CD4+ T Cells in the Proliferation of EBV-Infected T and NK Cells

Epstein-Barr virus (EBV), a ubiquitous B-lymphotropic herpesvirus, ectopically infects T or NK cells to cause severe diseases of unknown pathogenesis, including chronic active EBV infection (CAEBV) and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH). We developed xenograft models of CAEBV and EBV-HLH by transplanting patients' PBMC to immunodeficient mice of the NOD/Shi-scid/IL-2Rγnull strain. In these models, EBV-infected T, NK, or B cells proliferated systemically and reproduced histological characteristics of the two diseases. Analysis of the TCR repertoire expression revealed that identical predominant EBV-infected T-cell clones proliferated in patients and corresponding mice transplanted with their PBMC. Expression of the EBV nuclear antigen 1 (EBNA1), the latent membrane protein 1 (LMP1), and LMP2, but not EBNA2, in the engrafted cells is consistent with the latency II program of EBV gene expression known in CAEBV. High levels of human cytokines, including IL-8, IFN-γ, and RANTES, were detected in the peripheral blood of the model mice, mirroring hypercytokinemia characteristic to both CAEBV and EBV-HLH. Transplantation of individual immunophenotypic subsets isolated from patients' PBMC as well as that of various combinations of these subsets revealed a critical role of CD4+ T cells in the engraftment of EBV-infected T and NK cells. In accordance with this finding, in vivo depletion of CD4+ T cells by the administration of the OKT4 antibody following transplantation of PBMC prevented the engraftment of EBV-infected T and NK cells. This is the first report of animal models of CAEBV and EBV-HLH that are expected to be useful tools in the development of novel therapeutic strategies for the treatment of the diseases